Scalability

notes from here: https://www.lecloud.net/post/7994751381/scalability-for-dummies-part-2-database

1. Clones

• first golden rule for scalability: every server contains exactly the same codebase and does not store any:
  • user-related data
    • like sessions
    • profile pictures
  • data that changes\
    • app state
    • any sort of data that changes the next time the user visits the website

where to store data that needs to persist across visits (app state)

• sessions need to be stored in a centralized data store which is accessible to all your application servers
• can be:
  • external database
  • external persistent cache, like redis (better performance)

2. Database

• somewhere down the road your application gets slower and slower and finally breaks down. The reason? your database. it's MYSQL isn't it?